Professor Jichi Medical University, Saitama Medical Center Saitama, Saitama, Japan
Background: Bronchopulmonary dysplasia (BPD) is a serious complication in preterm infants, leading to increased mortality, neurological sequelae, and chronic obstructive respiratory conditions. However, many aspects of its pathogenesis remain unclear, and safe and effective treatments have not yet been established. In BPD models, epithelial-mesenchymal transition of type II alveolar cells has been reported to inhibit alveolar development, although the details are still unknown. On the other hand, IL-33 is a potent cytokine that is found in the nuclei of pulmonary epithelial cells and vascular endothelial cells. Upon injury, it induces Th2 cytokines and contributes to chronic inflammation and tissue remodeling. Despite its potential importance, research on the role of IL-33 in the pathogenesis of BPD has been insufficient. Objective: To elucidate the involvement of IL-33 in BPD using an animal model. Design/Methods: Newborn C57BL/6N mice were exposed to 60% oxygen for one week. They were then divided into three groups and administered intraperitoneal injections of either anti-IL-33 antibody (500 ng/mouse, every other day), recombinant IL-33 (rIL-33, 200 ng/mouse, every other day), or vehicle (IgG) for two weeks. A control group was housed in room air from birth. Lung histological examinations were conducted at 2 and 4 weeks of age. Additionally, immunohistochemical analyses, RT-qPCR, and Western blotting were performed to assess the expression of alpha-smooth muscle action (α-SMA) and other markers. Results: The hyperoxia-exposed group (HO) exhibited alveolar enlargement and a marked reduction in alveolar number at 4 weeks of age (Fig. 1), confirming successful establishment of the BPD model. Treatment with anti-IL-33 antibodies improved lung histology, whereas treatment with rIL-33 further deteriorated lung structure. In the HO group, immunohistochemical analyses showed increased expression of IL-33 and α-SMA, both of which were reduced by anti-IL-33 antibody treatment (Fig.2). RT-qPCR analysis revealed elevated ACTA2 gene expression, encoding α-SMA expression, in the hyperoxia group, which was suppressed in the anti-IL-33 antibody group (Fig.3).
Conclusion(s): Anti-IL-33 antibodies demonstrated efficacy in the BPD animal model. These findings suggest that IL-33 may contribute to BPD development by inhibiting alveolar formation through the epithelial-mesenchymal transition of type II alveolar epithelial cells.
Fig 1. Lung histology at 4 weeks of age using hematoxylin and eosin staining. Figure.001.jpeg(a)Control group, (b) Hyper-oxygen-exposed (HO) mice treated with vehicle, (c)HO mice treated with IL-33 antibody (200x magnification), (d) Mean alveolar area and radial alveolar count. The HO group showed enlarged alveolar size and a decreased number of alveoli compared to the control group. HO mice treated with IL-33 antibody demonstrated recovery in both alveolar number and size. (* indicates p < 0.05, ** p < 0.01, *** p < 0.001.)
Fig2. Lung IL-33 expression at 4 weeks of age analyzed by immunohistochemistry. Figure.002.jpeg(a) Control group, (b) Hyperoxia-exposed (HO) mice treated with vehicle, (c) HO mice treated with IL-33 antibody, (d) HO mice treated with recombinant IL-33(rIL33). Images are shown at 200x magnification. Red triangles indicate DAB-positive cells, with IL-33 expression localized in the nuclei of pulmonary epithelial cells. IL-33-positive cells were significantly increased in the HO group treated with vehicle, decreased in the HO group treated with IL-33 antibody, and markedly elevated in the group treated with rIL-33.
Fig3. Expression levels of ACTA2 in whole lung tissue at 4 weeks of age, measured by RT-qPCR. Figure.003.jpegACTA2 encodes alpha-smooth muscle actin. Hyper-oxygen exposed (HO) mice showed increased ACTA2 mRNA levels compared to the control group. Treatment with IL-33 antibody suppressed ACTA2 expression in HO mice. ( * indicates p < 0.05, ** p < 0.01.)
